package ch9;

/**
 * Created by lyk on 2016/10/15.
 * Package name: ch9
 * Porject name: untitled1
 */
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

/**
 * @version 1.33 2007-06-12
 * @author Cay Horstmann
 */
public class Calculator
{
    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                CalculatorFrame frame = new CalculatorFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
            }
        });
    }
}

/**
 * A frame with a calculator panel.
 */
class CalculatorFrame extends JFrame
{
    public CalculatorFrame()
    {
        setTitle("Calculator");
        CalculatorPanel panel = new CalculatorPanel();
        add(panel);
        pack();
    }
}

/**
 * A panel with calculator buttons and a result display.
 */
class CalculatorPanel extends JPanel
{
    public CalculatorPanel()
    {
        setLayout(new BorderLayout());

        result = 0;
        lastCommand = "=";
        start = true;

        // add the display

        display = new JButton("0");
        display.setEnabled(false);
        add(display, BorderLayout.NORTH);

        ActionListener insert = new InsertAction();
        ActionListener command = new CommandAction();

        // add the buttons in a 4 x 4 grid

        panel = new JPanel();
        panel.setLayout(new GridLayout(4, 4));

        addButton("7", insert);
        addButton("8", insert);
        addButton("9", insert);
        addButton("/", command);

        addButton("4", insert);
        addButton("5", insert);
        addButton("6", insert);
        addButton("*", command);

        addButton("1", insert);
        addButton("2", insert);
        addButton("3", insert);
        addButton("-", command);

        addButton("0", insert);
        addButton(".", insert);
        addButton("=", command);
        addButton("+", command);

        add(panel, BorderLayout.CENTER);
    }

    /**
     * Adds a button to the center panel.
     * @param label the button label
     * @param listener the button listener
     */
    private void addButton(String label, ActionListener listener)
    {
        JButton button = new JButton(label);
        button.addActionListener(listener);
        panel.add(button);
    }

    /**
     * This action inserts the button action string to the end of the display text.
     */
    private class InsertAction implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            String input = event.getActionCommand();
            if (start)
            {
                display.setText("");
                start = false;
            }
            display.setText(display.getText() + input);
        }
    }

    /**
     * This action executes the command that the button action string denotes.
     */
    private class CommandAction implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            String command = event.getActionCommand();

            if (start)
            {
                if (command.equals("="))
                {
                    display.setText(command);
                    start = false;
                }
                else lastCommand = command;
            }
            else
            {
                calculate(Double.parseDouble(display.getText()));
                lastCommand = command;
                start = true;
            }
        }
    }

    /**
     * Carries out the pending calculation.
     * @param x the value to be accumulated with the prior result.
     */
    public void calculate(double x)
    {
        if (lastCommand.equals("+")) result += x;
        else if (lastCommand.equals("-")) result -= x;
        else if (lastCommand.equals("*")) result *= x;
        else if (lastCommand.equals("/")) result /= x;
        else if (lastCommand.equals("=")) result = x;
        display.setText("" + result);
    }

    private JButton display;
    private JPanel panel;
    private double result;
    private String lastCommand;
    private boolean start;
}
